In the semiconductor manufacturing process, a circular substrate represented by a wafer is transported among a plurality of types of processing apparatuses and processed sequentially. Every time a substrate is to be loaded in each processing apparatus, its orientation must be adjusted in a predetermined direction. For this purpose, the substrate has a linear chip called an orientation flat, or a V- or U-shaped chip called a notch, in its peripheral portion, so as to indicate the orientation of the substrate. The orientation of the substrate is adjusted with reference to the chip.
As a technique for adjusting the orientation of the substrate, various types of techniques are conventionally proposed. For example, a method is proposed which holds a substrate by attracting its lower surface by a vacuum chuck and rotates the substrate. With this method, however, as a vacuum device comes into contact with the lower surface of the substrate, particles or the like attach to the lower surface of the substrate to influent the yield.
Japanese Patent Laid-Open No. 12-133696 proposes a method of rotating a substrate by clamping it with a clamp. According to this method, while attachment of particles or the like to the substrate can be decreased, the substrate must be reheld several times to detect a chip in the substrate, prolonging the aligning.
According to the method proposed in Japanese Patent Laid-Open No. 2002-368065, a substrate is supported in a non-contact manner with the Bernoulli chuck method. One driving roller and a plurality of idle rollers contact a plurality of peripheral portions of the substrate. The driving roller is rotated to rotate the substrate. With this method, however, a slip may occur between the substrate and driving roller. Even when the driving roller is stopped, the substrate may rotate by the inertia. Thus, the amount of rotation of the substrate cannot necessarily be controlled easily, and the accuracy of adjustment of the substrate orientation is not always high.